URFA, Turkey - A woman who defected from the Islamic State of Iraq and Syria (ISIS) has told her story for the first time to CNN, including how she was part of a ruthless female brigade of fighters.

The 25-year-old, who could not give her real name due to fears of reprisal, wanted to be known only as Khadija.

Her story begins as she was growing up in a "not overly conservative" family in Syria. Her parents even allowed her to go to school and get a college degree, and she went on to become an elementary school teacher, she told CNN.

When Syria's civil war began more than three years ago, she was one of those who protested against the government. But, she said, she began to lose her humanity when the unrest took a darker turn.

"Everything around us was chaos," she told CNN, adding that she wanted to run away from it all.

"My problem was I ran away to something uglier," she was quoted by CNN as saying.

Influenced by a charming Tunisian man she met online, she was lured by him to ISIS.

He told her that it was not a terrorist group, but it was going to "properly implement Islam".

On his prompting, Khadija moved to the city of Raqqa, where she got in touch with her cousin, whose husband had joined ISIS.

She brought her into the Khansa'a Brigade - termed by CNN as a fearsome, all-female police squad that patrolled the streets of the city to ensure women dress how ISIS want them to.

Women who broke these rules were lashed by the brigade's commander, a woman named Umm Hamza, whom Khadija described as "huge" and "not a normal female", as quoted by CNN.

Khadija's family tried to warn her against this path, but she did not take heed.

Finally, however, she started become afraid of what was happening, and even of herself, and question how she, a degree holder, had become like this.

She could not forget seeing a photo of a crucified 16-year-old boy, and wondered why she had joined a such a violent group.

"The worst thing I saw was a man getting his head hacked off in front of me," CNN quoted Khadija as saying.

She also baulked at how brutally ISIS treated women. "The foreign fighters are very brutal with women, even the ones they marry," she said as quoted by CNN. "(In some cases) the wife had to be taken to the emergency ward because of the... sexual violence."

Khadija decided to leave when they tried to coerce her into marriage, and was smuggled across the border to Turkey days before a United-States coalition began anti-ISIS air strikes on Syria.

Now, she faces a struggle to adapt to life outside ISIS, she said.

She still wears a niqab, partly to hide her identity, and partly as she does not want the change to be too abrupt, she told CNN, adding that she does not want to "become someone else" and turn anti-religion after regreting her indoctrination into radicalism.

Khadija spoke to CNN as she wanted the world to know the truth about ISIS, especially women.

"I don't want anyone else to be duped by them," CNN quoted her as saying.

At the end of her interview, she wondered how ISIS managed to make gains in Syrian society, telling CNN: "How did we allow them to come in? How did we allow them to rule us? There is a weakness in us."